block: ignore_bds_parents parameter for drain functions

In the future, bdrv_drained_all_begin/end() will drain all invidiual
nodes separately rather than whole subtrees. This means that we don't
want to propagate the drain to all parents any more: If the parent is a
BDS, it will already be drained separately. Recursing to all parents is
unnecessary work and would make it an O(n²) operation.

Prepare the drain function for the changed drain_all by adding an
ignore_bds_parents parameter to the internal implementation that
prevents the propagation of the drain to BDS parents. We still (have to)
propagate it to non-BDS parents like BlockBackends or Jobs because those
are not drained separately.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block/vvfat.c b/block/vvfat.c
index 4595f335b8..c7d2ed2d96 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -3134,6 +3134,7 @@ static void vvfat_qcow_options(int *child_flags, QDict *child_options,
 }
 
 static const BdrvChildRole child_vvfat_qcow = {
+    .parent_is_bds      = true,
     .inherit_options    = vvfat_qcow_options,
 };